S9S08SG8E2MTJ Datasheet, PDF(290/320 Page) Freescale Semiconductor, Inc – MC9S08SG8 MC9S08SG4 Data Sheet Addendum

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S9S08SG8E2MTJ Datasheet, PDF (290/320 Pages) Freescale Semiconductor, Inc – MC9S08SG8 MC9S08SG4 Data Sheet Addendum

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Appendix A Electrical Characteristics

The average chip-junction temperature (TJ) in ï°C can be obtained from:

where:

TJ = TA + (PD ï´ ï±JA)

Eqn. A-1

TA = Ambient temperature, ï°Cï

ï±JA = Package thermal resistance, junction-to-ambient, ï°C/Wï

PD = Pint ï«ï PI/Oï

Pint = IDD ï´ VDD, Watts â chip internal powerï

PI/O = Power dissipation on input and output pins â user determined

For most applications, PI/O ï¼ï¼ Pint and can be neglected. An approximate relationship between PD and TJ

(if PI/O is neglected) is:

PD = K ï¸ (TJ + 273ï°C)

Solving Equation A-1 and Equation A-2 for K gives:

Eqn. A-2

K = PD ï´ (TA + 273ï°C) + ï±JA ï´ (PD)2

Eqn. A-3

where K is a constant pertaining to the particular part. K can be determined from equation 3 by measuring

PD (at equilibrium) for a known TA. Using this value of K, the values of PD and TJ can be obtained by

solving Equation A-1 and Equation A-2 iteratively for any value of TA.

MC9S08SG8 MCU Series Data Sheet, Rev. 7

286

Freescale Semiconductor

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